Time and place relevant? [Insert LTPF list of countries, centuries and decades] Poland, during World War II, location is not essential to the puzzle

He = a scientist? yesish

Did he start the epidemics by by setting free bacteria/viruses? Was it an accident? While he was experimenting? Or did he do it on purpose? this, no to the rest

Did he start only one epidemy? difficult to say, assume one Or several? If the latter is the case, were they all the same disease or different types thereof? Or completely different diseases? completely different diseases are somehow relevant, but be careful

Using the singular form from now on, just for the sake of convenience:

Before it became an epidemy, was it a moderately spread disease? Was he trying to find a cure? no to both

Or was he the first person to have a certain disease that couldn't be cured and he passed it on to other people? no

Epidemics = infectuous disease? parasites? something else? human disease? veterinary? plant disease? Did he carry the disease himself? if so: did he know? Was he in Poland when he started the epidemics? Did he come to Poland? The Colorado Beetle relevant?

Sundowner: Epidemics = infectuous disease? this parasites? something else? human disease? this veterinary? plant disease? Did he carry the disease himself? if so: did he know? no to bothWas he in Poland when he started the epidemics? yesDid he come to Poland? no, he was Polish. But he emigrated after the warThe Colorado Beetle relevant? no

Twilightseeker: Did he kill a lot of Nazis with the epidemic and thereby save lot of Jews that would have otherwise been killed by the Nazis? no

Rbruma: Did anyone die from the disease during this epidemic? no, very good question. Did the survivors develop some sort of resistance to the disease so it was impossible for them afterwards to contract the disease? no

Did he start it knowingly? Was it part of the war effort? yes to both

Vesica: Location not essential...As in, it doesn't have to be Poland? Would any European country work as well? Only Eastern European? Only those invaded by Germany? This could happen in any country. Just wartime context is relevantGermany itelf?

Is WWII relevant? Only that it happened during the war and to settle the contextAre concetration camps revelant? Mildly

He is a yes-ish scientist: Doctor? yesMedical professional? Academic in a medical field? probably also this. He had more specific knowledge than any usual doctorBiology? Sociology? (I don't think this existed yet but...)Epidemiology? also a bit of this

Epidemic of a single disease, yes? yesBut other diseases are relevant? yesish - one other "disease", for svv of "disease"Are the others related to the one? YESLike Cow Pox and Small Pox? but not this way. Explore!

Did the "saved" people have the disease when their lives were saved? After? Very long after?

Did the epidemic disease help them create antibodies that saved them from a later disease(s)? Did the symptoms make them less susceptible to other diseases?

Did the epidemic disease make them sick? Very sick, in bed? Feeling a little unwell? Or caused some sort of sickness in their body, but at an almost unnoticable level?

Is the epidemic disease unique to humans? In this epidemic, did it originate in humans?

Conditions of war time - Are these relevant: Food shortages? Lack of clean water? Social dislocation? Loss of heating for homes? Being exposed to immigrants from other countries (and their diseases)? Actual fighting by troops? Bombings?

Were the "saved" people saved all at the same time? Over a period of time? Were they all in the same place?

Twilightseeker: Did the presence or existence a disease/diseases prevent some kind of war crime? prevent general war-induced slaughter/killing? was it widely known that this disease(s) was/were dangerous? yes to all

Doriana: Was he ordered to do this by some higher authority? Did authorities or officials know what he was doing? Did they approve it? all are irrelevant, assume he did it on his own

Did he save lives in general? Or the lives of a certain group of people? this Lives of unborn children? not in this meaning of group, thoughField hospitals relevant? no

Did the "saved" people have the disease when their lives were saved? yesAfter? Very long after?

Did the epidemic disease help them create antibodies that saved them from a later disease(s)? noDid the symptoms make them less susceptible to other diseases? no

Did the epidemic disease make them sick? no!Very sick, in bed? Feeling a little unwell? Or caused some sort of sickness in their body, but at an almost unnoticable level? this or even less than this

Is the epidemic disease unique to humans? noIn this epidemic, did it originate in humans? activity of our man affected humans only

Conditions of war time - Are these relevant: Food shortages? Lack of clean water? Social dislocation? Loss of heating for homes? Being exposed to immigrants from other countries (and their diseases)? Actual fighting by troops? this but not only thisBombings?

Were the "saved" people saved all at the same time? Over a period of time? during the whole wartimeWere they all in the same place? yesish

The persons that became sick: People who were about to join the troops? Because they were forced? People who were already fighting? Prisoners of war?

Did the sickness allow them to stay at home / go back home? If they hadn't become sick, would they have probably died in the war (due to them fighting)? Or even surely (because they would've been executed)?

If they were allowed to stay away from the war, was it more because the persons who decided that were afraid of the disease spreading further? Or because the disease would've affected the performance of the infected persons (assuming they were soldiers)?

So, the disease didn't really make the infected persons look sick, right? Were healthy persons able to stay away by claiming that they had the disease?

Was the general public even aware of the disease at that time?

While not being deadly, did the disease lead to any sort of long-time or permanent impairment?

Potato: The persons that became sick: People who were about to join the troops? Because they were forced? People who were already fighting? Prisoners of war? no to all

Did the sickness allow them to stay at home / go back home? FA If they hadn't become sick, would they have probably died in the war some probably would (due to them fighting but not for this reason)? Or even surely (because they would've been executed)? some probably would be executed, too.

If they were allowed to stay away from the war literally correct, but the same FA, was it more because the persons who decided that were afraid of the disease spreading further? YES! Or because the disease would've affected the performance of the infected persons (assuming they were soldiers)? no

So, the disease didn't really make the infected persons look sick, right? yes indeed. Were healthy persons able to stay away by claiming that they had the disease? Yes, they were.

Was the general public even aware of the disease at that time? The enemy knew and only that's relevant

While not being deadly, did the disease lead to any sort of long-time or permanent impairment? no

Not sure if this is too far-fetched, but did the enemy refuse to carry on fighting due to being afraid of catching the disease?

Probably even more far-fetched, but did the epidemy actually exist? Or was it all just made up with the aim of frightening the enemy by the rumor of a new epidemy? One that was similar to an actual and highly dangerous one?

You said that the disease affects the brain/nervous system, the circulatory system and the endocrine system. Does the disease mainly have an impact on the psyche?

Potato: Not sure if this is too far-fetched, but did the enemy refuse to carry on fighting due to being afraid of catching the disease? yesish - yope

Probably even more far-fetched, but did the epidemy actually exist? Noish! Or was it all just made up with the aim of frightening the enemy by the rumor of a new epidemy? Yes it was indeed One that was similar to an actual and highly dangerous one? This is all very OTRT, but some important details are wrong or missing

You said that the disease affects the brain/nervous system, the circulatory system and the endocrine system. Does the disease mainly have an impact on the psyche? again - which disease? The dangerous one is a normal, physical disease.

Are there two diseases, right? Is there a scenario like the following: a very contagious disease had some symptoms, easily recognized by the enemy; so our hero created a variation that exhibited the same apparent symptoms, but of a condition that was not life-threatening? And the enemy considered this "epidemic" to be that of the real one? Is it at least OTRT?

Rbruma: Are there two diseases, right? yes Is there a scenario like the following: a very contagious disease had some symptoms, easily recognized by the enemy; yes so our hero created a variation that exhibited the same apparent symptoms, but of a condition that was not life-threatening? noish And the enemy considered this "epidemic" to be that of the real one? yes Is it at least OTRT? This is very OTRT, only the part of what the man actually did is inaccurate.

Did he manage to turn the region into a kind of sanctuary that wasn't allowed to be attacked? And people from other regions went there to escape from war?

Evacuation relevant? Were the people who pretended to have the disease allowed to go to some place that was specifically designed for curing their disease (like a leper colony)? And they stayed there until the war was over (or even longer)?

Potato: Did he manage to turn the region into a kind of sanctuary that wasn't allowed to be attacked? In a sense, yes. The Nazis were afraid to enter the area due to the "disease". And people from other regions went there to escape from war? Unknown, but possible.

Evacuation relevant? no Were the people who pretended to have the disease allowed to go to some place that was specifically designed for curing their disease (like a leper colony)? And they stayed there until the war was over (or even longer)? see above, people stayed safely at homes.

Okay, let's try another variation: Somewhere in Poland, during WWII there is a doctor? And he starts a rumor that the citizens of his town (part of the country, the whole country) have X disease? And X disease can be passed from person to person? And the Nazis are sore afraid? Because X disease is fatal? Highly contagious? Disfiguring?

This ruse works because... There is another epidemic, Y disease, plaguing the citizens? Y disease is not fatal (serious, life-threatening)? But it has symptoms that can be mistaken for symptoms of X disease?

So the Nazis believe the X outbreak is real and stay away?

X and Y diseases are related? But are not Small Pox and Cow Pox?

And now...for a really long list of diseases that can be passed from person to person...

What's scary is how easy it was for me to come up with once I started thinking. I've always thought epidemiology was cool and have looked at postings for the CDC. Don't want to live in Atlanta though...

Vesica: Somewhere in Poland, during WWII there is a doctor? yesAnd he starts a rumor that the citizens of his town (part of the country, the whole country) have X disease? He did more. Would Nazis just believe his word, no checking the rumor?And X disease can be passed from person to person? yesAnd the Nazis are sore afraid? yesBecause X disease is fatal? yes Highly contagious? Disfiguring?

This ruse works because... There is another epidemic, Y disease, plaguing the citizens? yope, exploreY disease is not fatal (serious, life-threatening)? yes. It has very little impact on people, but...But it has symptoms that can be mistaken for symptoms of X disease? YOPE - explore! Definitely it can be mistaken for typhoid, but WHY?

So the Nazis believe the X outbreak is real and stay away? yes

X and Y diseases are related? somehow related, explore the yope for symptoms and you will knowBut are not Small Pox and Cow Pox? indeed

Vesica: Relevant typhoid symptom: Fever? Sweating? Cough? Diarrhea? Rash of red spots (though wiki says this happens in only 1/3 of cases)? none, as to my knowledge.HINT: The non-harmful bacteria and typhoid give exactly the same result of blood analysis, and that's all relevant knowledge about symptoms. Only thing left is what the doctor did to convince Nazis that there's typhoid epidemia?

Vesica: Did the doctor claim he didn't know what was wrong with the people? noAnd brought them to Nazi docs for evaluation? but yesWhen the tests were run - it looked like typhoid? yes, that was the concept

Did the doctor draw the blood? yesDid the Nazis? and yesWere the Nazis checking for illness or something else? for illness. They realized that there's epidemics but not more people die than usually and decided to check.

Did everyone's blood get checked? Or just certain people? This. Certain people of those about whom the doctor claimed they were ill

And now for some questions…Did the doctor start the other epidemic (Disease Y)? Was it present because of the wartime conditions? Or was it endemic to the area?

Is Disease Y contagious? Passed from person to person?

Tyhpoid is caused by a type of Salmonella bacteria, yes? But there are other Salmonella bacteria that cause other illnesses in humans? Such as food poisioning?

Hey WAIT! Did the doctor deliberately give a few folks Salmonella food poisoning? And then send those folks only for testing? And for some reason the Nazis could not tell the difference, only that they were Salmonella bacteria? Did the right equipment not exist to see the difference? Were they using a chemical or indicator test? That could not tell the difference? Is how they read the blood test relevant? Did the doctor tamper with the chemicals/equipment/means of reading the blood test?

Forgive me not answering the specific questions about the disease and bacteria - but help is soon to come.

Tyhpoid is caused by a type of Salmonella bacteria, yes? But there are other Salmonella bacteria that cause other illnesses in humans? Such as food poisioning?

Hey WAIT! Did the doctor deliberately give a few folks Salmonella food poisoning? not exacly, but close enough.And then send those folks only for testing? And for some reason the Nazis could not tell the difference, only that they were Salmonella bacteria? Did the right equipment not exist to see the difference? Were they using a chemical or indicator test? That could not tell the difference? Is how they read the blood test relevant? Did the doctor tamper with the chemicals/equipment/means of reading the blood test?

******SPOILER********* During World War II, a Polish doctor used the Proteus OX19 bacteria to masquerade as typhoid, as the presence of the bacteria made blood tests results look like those of typhoid. He deliberately give the Proteus OX19 to people from the area. There is one more interesting story about that. When the Nazis wanted to check the rumor (they saw that no more people die than usually), the doctor made a big alcohol party in the town hall. The main Nazi doctor from the checking team stayed on the party and sent two young trainees to the hospital. Polish doctor previously moved the hospital to the weakest and most ruined cottage in the area, to make humble impression. Then he placed in the "hospital" the weakest, old people and taught them what to tell to Nazis. The trainees made a simple blood test, noticed fever and spots and diagnosed typhoid.

Thanks to Vesica for her persistence and guessing it, congrats also to Fishbones, who emailed me a correct solution.